1. Field of the Invention
The present invention relates to a device and a method for generating a three-dimensional model and a recording medium storing the three-dimensional model generation method.
2. Description of the Related Art
Conventionally, various techniques for generating a realistic three-dimensional (hereinafter referred to as “3-D”) model as an image have been proposed.
For example, Publication 1 (Masahide KANEKO et al., “Encoding of Face Moving Picture Based on Detection of Change in Geometry and Geometric 3-D Model”, IE87-101) describes the following technique. A rough geometric 3-D model, which has been previously created using general knowledge of the geometry of a face, is projected onto an image of a target face. Texture to be mapped to the 3-D model is generated based on the correspondence between the coordinates of the projected 3-D model and the target face image. Thus, the texture-mapped 3-D model is obtained. The texture-mapped 3-D model may be optionally modified to generate facial expressions. Also, the texture-mapped 3-D model may be projected in a direction different from that for the previous projection by which the input image is obtained, so that a pseudo-image when viewed from the different direction can be displayed.
There is an alternative way to generate a more realistic 3-D model. A rough geometric 3-D model, which has been previously created using knowledge of the geometry of a target object, is projected onto an image of the target object. The coordinates of vertexes or feature points of the projected rough geometric 3-D model are fine adjusted in association with deformation or the like so as to match the coordinates of the corresponding vertexes or feature points of the target object image.
For example, Japanese Laid-Open Publication No. 4-289976 discloses the following technique. Two dimensional (hereinafter referred to as “2-D”) graphic information on a target 3-D object and a basic geometric 3-D model approximate to the basic geometry of the target object are input. The operator correlates a feature point of the 2-D graphic information with a control point of the basic geometric 3-D model, thereby deforming the basic geometric 3-D model to obtain the desired geometric 3-D model.
Further, simple geometric 3-D models or 3-D models obtained by any technique may be handled as components and may be combined to generate a complex 3-D model. The resulting 3-D models may be handled as components and may be further combined in to a more complex 3-D model.
In general, when a picture is taken of an object, the shooting direction is designated as, for example, “from the front” or “from this direction”. Unfortunately, the actual shooting direction is usually shifted from the exact designated direction. For example, when a picture is taken of a human face, the object unintentionally orients slightly upward or downward due to his/her habit even if the object intends to face to “the front”. Some systems require that an image taken from the front be used as texture data which is to be mapped to a 3-D model. In this case, the object must be forced to face “the front” exactly by some method. This makes it impossible to easily take a picture. A picture of a face which has been already taken by non-specialized people cannot be used.
Even if such problems are solved, there are still other problems. The outline of a rough geometric model may not match the outline of an actual image of a target object. In this case, the color of the background or the like creeps into the vicinity of the outline of the generated 3-D model, rendering the color of the model unnatural.
In the above-described conventional techniques, a plurality of different geometric models are required. Texture needs to be prepared for each geometric model, is resulting in a great load.
In the conventional techniques where two or more components are combined to generate a 3-D model, the combination method poses problems. Specifically, what is combined therein is position, size, or the like. Geometry itself may be problematic. For example, consider the case where a 3-D model of a face is combined with a 3-D model of the hair. If the face is too large, the hair unnaturally appears to be buried in the face. Inversely, if the hair is too large, the hair unnaturally appears to hover. Further, if the geometry of an upper side (border) of the face does not match the geometry of a lower side of the hair, part of the hair may hover or be buried, resulting in an unnatural image. It is needless to say that position mismatch causes the image to be unnatural even if the size and the geometry are natural.
Conventionally, the operator adjusts the sizes, positions, and geometry of the vicinity of border portions in order to remove the unnaturalness. Such adjustment is painstaking and time-consuming. Alternatively, a table for the adjustment may be prepared in advance. The combination of components is adjusted with reference to the table. Again, a similar problem arises in which the preparation of the table is painstaking and time-consuming.
A more realistic 3-D model requires a larger number of rough geometric models. The larger the number of rough geometric models, the greater the load on the operator selecting the models.
A face is an object having complex geometry. The generation of a realistic 3-D model of a face is a painstaking task even with the above-described conventional techniques.